OpenGL 入门基础教程 —— 加载obj模型

短命女 2023-10-17 13:39 76阅读 0赞

参考资料：http://www.opengl-tutorial.org/cn/beginners-tutorials/tutorial-7-model-loading/

**知识点1：obj模型**

较为简单的obj模型：

# Blender3D v249 OBJ File: untitled.blend
    # www.blender3d.org
    mtllib cube.mtl
    v 1.000000 -1.000000 -1.000000
    v 1.000000 -1.000000 1.000000
    v -1.000000 -1.000000 1.000000
    v -1.000000 -1.000000 -1.000000
    v 1.000000 1.000000 -1.000000
    v 0.999999 1.000000 1.000001
    v -1.000000 1.000000 1.000000
    v -1.000000 1.000000 -1.000000
    vt 0.748573 0.750412
    vt 0.749279 0.501284
    vt 0.999110 0.501077
    vt 0.999455 0.750380
    vt 0.250471 0.500702
    vt 0.249682 0.749677
    vt 0.001085 0.750380
    vt 0.001517 0.499994
    vt 0.499422 0.500239
    vt 0.500149 0.750166
    vt 0.748355 0.998230
    vt 0.500193 0.998728
    vt 0.498993 0.250415
    vt 0.748953 0.250920
    vn 0.000000 0.000000 -1.000000
    vn -1.000000 -0.000000 -0.000000
    vn -0.000000 -0.000000 1.000000
    vn -0.000001 0.000000 1.000000
    vn 1.000000 -0.000000 0.000000
    vn 1.000000 0.000000 0.000001
    vn 0.000000 1.000000 -0.000000
    vn -0.000000 -1.000000 0.000000
    usemtl Material_ray.png
    s off
    f 5/1/1 1/2/1 4/3/1
    f 5/1/1 4/3/1 8/4/1
    f 3/5/2 7/6/2 8/7/2
    f 3/5/2 8/7/2 4/8/2
    f 2/9/3 6/10/3 3/5/3
    f 6/10/4 7/6/4 3/5/4
    f 1/2/5 5/1/5 2/9/5
    f 5/1/6 6/10/6 2/9/6
    f 5/1/7 8/11/7 6/10/7
    f 8/11/7 7/12/7 6/10/7
    f 1/2/8 2/9/8 3/13/8
    f 1/2/8 3/13/8 4/14/8

较为复杂的obj模型(从网上自己下载的一个)：有一万多行的数据，模型较为复杂

其中：

\#是注释标记，就像C++中的//  
usemtl和mtlib描述了模型的外观。本课用不到。  
v代表顶点，后面跟 x,y,z 分量  
vt代表顶点的纹理坐标，后面跟 u，v分量  
vn代表顶点的法线，后面跟法线的向量 x,y,z  
f代表面

**f比较麻烦。**例如f 8/11/7 7/12/7 6/10/7：

8/11/7描述了三角形的第一个顶点  
7/12/7描述了三角形的第二个顶点  
6/10/7描述了三角形的第三个顶点  
对于第一个顶点：8指向要用的顶点。此例中是-1.000000 1.000000 -1.000000（索引从1开始，和C++中从0开始不同）11指向要用的纹理坐标。此例中是0.748355 0.998230。7指向要用的法线。此例中是0.000000 1.000000 -0.000000。  
我们称这些数字为索引。若几个顶点共用同一个坐标，索引就显得很方便，文件中只需保存一个”V”，可以多次引用，节省了存储空间。  
  
其弊端在于我们无法让OpenGL混用顶点、纹理和法线索引。因此本课采用的方法是创建一个标准的、未加索引的模型。

**注意点：**在网上下载了很多的obj模型，但是能用的只有几个，总是提示数组维度出现错误，后来发现他的obj文件中：

f 54740 54741 54742 54743  
f 54744 54747 54746 54745  
f 54740 54744 54745 54741  
f 54741 54745 54746 54742  
f 54742 54746 54747 54743  
f 54744 54740 54743 54747

这样表示的方法不适用于此简单的obj加载函数。

**加载obj的函数：**

#include <vector>
    #include <stdio.h>
    #include <string>
    #include <cstring>
    
    #include <glm/glm.hpp>
    
    #include "objloader.hpp"
    
    // Very, VERY simple OBJ loader.
    // Here is a short list of features a real function would provide : 
    // - Binary files. Reading a model should be just a few memcpy's away, not parsing a file at runtime. In short : OBJ is not very great.
    // - Animations & bones (includes bones weights)
    // - Multiple UVs
    // - All attributes should be optional, not "forced"
    // - More stable. Change a line in the OBJ file and it crashes.
    // - More secure. Change another line and you can inject code.
    // - Loading from memory, stream, etc
    
    bool loadOBJ(
    	const char * path, 
    	std::vector<glm::vec3> & out_vertices, 
    	std::vector<glm::vec2> & out_uvs,
    	std::vector<glm::vec3> & out_normals
    ){
    	printf("Loading OBJ file %s...\n", path);
    
    	std::vector<unsigned int> vertexIndices, uvIndices, normalIndices; //临时存储量
    	std::vector<glm::vec3> temp_vertices; 
    	std::vector<glm::vec2> temp_uvs;
    	std::vector<glm::vec3> temp_normals;
    
    
    	FILE * file = fopen(path, "r"); //打开obj文件
    	if( file == NULL ){
    		printf("Impossible to open the file ! Are you in the right path ? See Tutorial 1 for details\n");
    		getchar();
    		return false;
    	}
    
    	while( 1 ){ //总是执行
    
    		char lineHeader[128];
    		// read the first word of the line
    		int res = fscanf(file, "%s", lineHeader);
    		if (res == EOF)
    			break; // EOF = End Of File. Quit the loop.
    
    		// else : parse lineHeader
    		//判断每行的首字母是哪种，对应存储到不同的数组中去
    		if ( strcmp( lineHeader, "v" ) == 0 ){
    			glm::vec3 vertex;
    			fscanf(file, "%f %f %f\n", &vertex.x, &vertex.y, &vertex.z );
    			temp_vertices.push_back(vertex);
    		}else if ( strcmp( lineHeader, "vt" ) == 0 ){
    			glm::vec2 uv;
    			fscanf(file, "%f %f\n", &uv.x, &uv.y );
    			uv.y = -uv.y; // Invert V coordinate since we will only use DDS texture, which are inverted. Remove if you want to use TGA or BMP loaders.
    			temp_uvs.push_back(uv);
    		}else if ( strcmp( lineHeader, "vn" ) == 0 ){
    			glm::vec3 normal;
    			fscanf(file, "%f %f %f\n", &normal.x, &normal.y, &normal.z );
    			temp_normals.push_back(normal);
    		}else if ( strcmp( lineHeader, "f" ) == 0 ){
    			std::string vertex1, vertex2, vertex3;
    			unsigned int vertexIndex[3], uvIndex[3], normalIndex[3];
    			int matches = fscanf(file, "%d/%d/%d %d/%d/%d %d/%d/%d\n", &vertexIndex[0], &uvIndex[0], &normalIndex[0], &vertexIndex[1], &uvIndex[1], &normalIndex[1], &vertexIndex[2], &uvIndex[2], &normalIndex[2] );
    			if (matches != 9){
    				printf("File can't be read by our simple parser :-( Try exporting with other options\n");
    				return false;
    			}
    			vertexIndices.push_back(vertexIndex[0]);
    			vertexIndices.push_back(vertexIndex[1]);
    			vertexIndices.push_back(vertexIndex[2]);
    			uvIndices    .push_back(uvIndex[0]);
    			uvIndices    .push_back(uvIndex[1]);
    			uvIndices    .push_back(uvIndex[2]);
    			normalIndices.push_back(normalIndex[0]);
    			normalIndices.push_back(normalIndex[1]);
    			normalIndices.push_back(normalIndex[2]);
    		}else{
    			// Probably a comment, eat up the rest of the line，其它内容未知放在此处，也可能会造成溢出的情况，因为大小只有1000
    			char stupidBuffer[1000];
    			fgets(stupidBuffer, 1000, file);
    		}
    
    	}
    
    	// For each vertex of each triangle，将读入的数据存储到对应的VAO中
    	for( unsigned int i=0; i<vertexIndices.size(); i++ ){
    
    		// Get the indices of its attributes
    		unsigned int vertexIndex = vertexIndices[i];
    		unsigned int uvIndex = uvIndices[i];
    		unsigned int normalIndex = normalIndices[i];
    		
    		// Get the attributes thanks to the index
    		glm::vec3 vertex = temp_vertices[ vertexIndex-1 ];
    		glm::vec2 uv = temp_uvs[ uvIndex-1 ];
    		glm::vec3 normal = temp_normals[ normalIndex-1 ];
    		
    		// Put the attributes in buffers
    		out_vertices.push_back(vertex);
    		out_uvs     .push_back(uv);
    		out_normals .push_back(normal);
    	
    	}
    
    	return true;
    }
    
    
    #ifdef USE_ASSIMP // don't use this #define, it's only for me (it AssImp fails to compile on your machine, at least all the other tutorials still work)
    
    // Include AssImp
    #include <assimp/Importer.hpp>      // C++ importer interface
    #include <assimp/scene.h>           // Output data structure
    #include <assimp/postprocess.h>     // Post processing flags
    
    bool loadAssImp(
    	const char * path, 
    	std::vector<unsigned short> & indices,
    	std::vector<glm::vec3> & vertices,
    	std::vector<glm::vec2> & uvs,
    	std::vector<glm::vec3> & normals
    ){
    
    	Assimp::Importer importer;
    
    	const aiScene* scene = importer.ReadFile(path, 0/*aiProcess_JoinIdenticalVertices | aiProcess_SortByPType*/);
    	if( !scene) {
    		fprintf( stderr, importer.GetErrorString());
    		getchar();
    		return false;
    	}
    	const aiMesh* mesh = scene->mMeshes[0]; // In this simple example code we always use the 1rst mesh (in OBJ files there is often only one anyway)
    
    	// Fill vertices positions
    	vertices.reserve(mesh->mNumVertices);
    	for(unsigned int i=0; i<mesh->mNumVertices; i++){
    		aiVector3D pos = mesh->mVertices[i];
    		vertices.push_back(glm::vec3(pos.x, pos.y, pos.z));
    	}
    
    	// Fill vertices texture coordinates
    	uvs.reserve(mesh->mNumVertices);
    	for(unsigned int i=0; i<mesh->mNumVertices; i++){
    		aiVector3D UVW = mesh->mTextureCoords[0][i]; // Assume only 1 set of UV coords; AssImp supports 8 UV sets.
    		uvs.push_back(glm::vec2(UVW.x, UVW.y));
    	}
    
    	// Fill vertices normals
    	normals.reserve(mesh->mNumVertices);
    	for(unsigned int i=0; i<mesh->mNumVertices; i++){
    		aiVector3D n = mesh->mNormals[i];
    		normals.push_back(glm::vec3(n.x, n.y, n.z));
    	}
    
    
    	// Fill face indices
    	indices.reserve(3*mesh->mNumFaces);
    	for (unsigned int i=0; i<mesh->mNumFaces; i++){
    		// Assume the model has only triangles.
    		indices.push_back(mesh->mFaces[i].mIndices[0]);
    		indices.push_back(mesh->mFaces[i].mIndices[1]);
    		indices.push_back(mesh->mFaces[i].mIndices[2]);
    	}
    	
    	// The "scene" pointer will be deleted automatically by "importer"
    
    }
    
    #endif

C++代码：

1：加载了不同的模型：是一个剑士

2：加载obj模型，理论上就是得到所需的顶点、UV、法线、Face数据，无需再逐个的进行定义数组

// Include standard headers
    #include <stdio.h>
    #include <stdlib.h>
    #include <vector>
    
    // Include GLEW
    #include <GL/glew.h>
    
    // Include GLFW
    #include <glfw3.h>
    GLFWwindow* window;
    
    // Include GLM
    #include <glm/glm.hpp>
    #include <glm/gtc/matrix_transform.hpp>
    #include <glm/gtx/transform.hpp>
    using namespace glm;
    
    #include <common/shader.hpp>
    #include <common/texture.hpp>
    #include <common/controls.hpp>
    #include <common/objloader.hpp>
    
    int main( void )
    {
    	// Initialise GLFW
    	if( !glfwInit() )
    	{
    		fprintf( stderr, "Failed to initialize GLFW\n" );
    		getchar();
    		return -1;
    	}
    
    	glfwWindowHint(GLFW_SAMPLES, 4);
    	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    	glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // To make MacOS happy; should not be needed
    	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    
    	// Open a window and create its OpenGL context
    	window = glfwCreateWindow( 1024, 768, "Tutorial 07 - Model Loading", NULL, NULL);
    	if( window == NULL ){
    		fprintf( stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n" );
    		getchar();
    		glfwTerminate();
    		return -1;
    	}
    	glfwMakeContextCurrent(window);
    
    	// Initialize GLEW
    	glewExperimental = true; // Needed for core profile
    	if (glewInit() != GLEW_OK) {
    		fprintf(stderr, "Failed to initialize GLEW\n");
    		getchar();
    		glfwTerminate();
    		return -1;
    	}
    
    	// Ensure we can capture the escape key being pressed below
    	glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);
        // Hide the mouse and enable unlimited mouvement
        glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);
        
        // Set the mouse at the center of the screen
        glfwPollEvents();
        glfwSetCursorPos(window, 1024/2, 768/2);
    
    	// Dark blue background
    	glClearColor(0.0f, 0.0f, 0.4f, 0.0f);
    
    	// Enable depth test
    	glEnable(GL_DEPTH_TEST);
    	// Accept fragment if it closer to the camera than the former one
    	glDepthFunc(GL_LESS); 
    
    	// Cull triangles which normal is not towards the camera
    	glEnable(GL_CULL_FACE);
    
    	GLuint VertexArrayID;
    	glGenVertexArrays(1, &VertexArrayID);
    	glBindVertexArray(VertexArrayID);
    
    	// Create and compile our GLSL program from the shaders
    	GLuint programID = LoadShaders( "TransformVertexShader.vertexshader", "TextureFragmentShader.fragmentshader" );
    
    	// Get a handle for our "MVP" uniform
    	GLuint MatrixID = glGetUniformLocation(programID, "MVP");
    
    	// Load the texture
    	//GLuint Texture = loadBMP_custom("47.bmp");
    	GLuint Texture = loadDDS("avatar_a_t00_ori.DDS");
    	
    	// Get a handle for our "myTextureSampler" uniform
    	GLuint TextureID  = glGetUniformLocation(programID, "myTextureSampler");
    
    	// Read our .obj file
    	std::vector<glm::vec3> vertices;
    	std::vector<glm::vec2> uvs;
    	std::vector<glm::vec3> normals; // Won't be used at the moment.
    	bool res = loadOBJ("56.obj", vertices, uvs, normals);
    
    	// Load it into a VBO
    
    	GLuint vertexbuffer; //绑定对应的顶点数组
    	glGenBuffers(1, &vertexbuffer);
    	glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
    	glBufferData(GL_ARRAY_BUFFER, vertices.size() * sizeof(glm::vec3), &vertices[0], GL_STATIC_DRAW);
    
    	GLuint uvbuffer;
    	glGenBuffers(1, &uvbuffer);//绑定对应的uv数组
    	glBindBuffer(GL_ARRAY_BUFFER, uvbuffer);
    	glBufferData(GL_ARRAY_BUFFER, uvs.size() * sizeof(glm::vec2), &uvs[0], GL_STATIC_DRAW);
    
    	do{
    
    		// Clear the screen
    		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    
    		// Use our shader
    		glUseProgram(programID);
    
    		// Compute the MVP matrix from keyboard and mouse input
    		computeMatricesFromInputs();
    		glm::mat4 ProjectionMatrix = getProjectionMatrix();
    		glm::mat4 ViewMatrix = getViewMatrix();
    		glm::mat4 ModelMatrix = glm::mat4(0.1);
    		glm::mat4 myScalingMatrix = glm::scale(glm::vec3(0.1f, 0.1f ,0.1f));//缩放矩阵
    		glm::mat4 MVP = ProjectionMatrix * ViewMatrix * ModelMatrix*myScalingMatrix;
    
    		// Send our transformation to the currently bound shader, 
    		// in the "MVP" uniform
    		glUniformMatrix4fv(MatrixID, 1, GL_FALSE, &MVP[0][0]);
    
    		// Bind our texture in Texture Unit 0
    		glActiveTexture(GL_TEXTURE0);
    		glBindTexture(GL_TEXTURE_2D, Texture);
    		// Set our "myTextureSampler" sampler to user Texture Unit 0
    		glUniform1i(TextureID, 0);
    
    		// 1rst attribute buffer : vertices
    		glEnableVertexAttribArray(0);
    		glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
    		glVertexAttribPointer(
    			0,                  // attribute
    			3,                  // size
    			GL_FLOAT,           // type
    			GL_FALSE,           // normalized?
    			0,                  // stride
    			(void*)0            // array buffer offset
    		);
    
    		// 2nd attribute buffer : UVs
    		glEnableVertexAttribArray(1);
    		glBindBuffer(GL_ARRAY_BUFFER, uvbuffer);
    		glVertexAttribPointer(
    			1,                                // attribute
    			2,                                // size
    			GL_FLOAT,                         // type
    			GL_FALSE,                         // normalized?
    			0,                                // stride
    			(void*)0                          // array buffer offset
    		);
    
    		// Draw the triangle !
    		glDrawArrays(GL_TRIANGLES, 0, vertices.size() );
    
    		glDisableVertexAttribArray(0);
    		glDisableVertexAttribArray(1);
    
    		// Swap buffers
    		glfwSwapBuffers(window);
    		glfwPollEvents();
    
    	} // Check if the ESC key was pressed or the window was closed
    	while( glfwGetKey(window, GLFW_KEY_ESCAPE ) != GLFW_PRESS &&
    		   glfwWindowShouldClose(window) == 0 );
    
    	// Cleanup VBO and shader
    	glDeleteBuffers(1, &vertexbuffer);
    	glDeleteBuffers(1, &uvbuffer);
    	glDeleteProgram(programID);
    	glDeleteTextures(1, &TextureID);
    	glDeleteVertexArrays(1, &VertexArrayID);
    
    	// Close OpenGL window and terminate GLFW
    	glfwTerminate();
    
    	return 0;
    }